In general, an inkjet printer is equipped with an ink cartridge for connecting with its print head. The inkjet printer must be capable of continuously and uniformly supplying ink during its printing process. The ink cartridges generally use the capillary force of a porous body, such as a sponge, to store ink liquid and control the ink supply. For example, Chinese patent publication No. 1334198A discloses an ink cartridge with a spillover dam board. The ink cartridge includes a housing enclosing a wick chamber. The housing includes a top wall and an ink chamber. A fluid conduit connects the ink chamber and the wick chamber. The outer surface of the top wall of the housing is formed with a recess. A vent opening through the top wall of the wick chamber, at the recess, provides fluid communication between the wick chamber and the recess. A covering over the top surface of the housing encloses the recess. An outlet opening through an outer wall other than the top wall of the wick chamber provides fluid communication for the ink to flow from the wick chamber. One end of an overflow tube is in fluid communication with the recess in the top wall of the housing. The other end of the overflow tube opens to the ambient environment at another point on the exterior of the housing, such as near the outlet opening. A dam in the recess, between the vent opening and the one end of the overflow tube, impedes, but does not completely obstruct, the flow of spillover ink from the vent opening into the overflow tube. Generally, with this type of ink cartridge, it is hard to prevent residual ink from remaining therein. In addition, its production cost is high, and it is not easy to keep a state of constant negative pressure in the ink cartridge.
Further, an improved ink cartridge can be obtained as a result of the improvement of the ink cartridge structure. Such an improved ink cartridge can store ink liquid and control the ink supply merely by its geometric structure. For example, Chinese utility model patent No. 02227387.5 discloses an ink cartridge which can cause its whole inner chamber to be in a state of negative pressure, and which can further ensure that the ink outlet is in a sealing state to prevent ink from leaking out when the ink cartridge has been detached from a printer. The ink cartridge includes an ink storing chamber, a pressure regulating mechanism, a sealing member, and a spring. The pressure regulating mechanism is located in the ink storing chamber and includes a front valve body, a rear valve body, a valve membrane, a cover and a spring. The front valve body and the rear valve body closely connect with each other and form a space, with the valve membrane disposed there between. The spring is between the valve membrane and the front valve body. The rear valve body is formed with an air groove, a concave hole is formed on a protrusion which is on the centre of the bottom surface of the air groove. The valve membrane is provided with a small circular hole which has a protruding rim, and which is pressed in the concave hole of the rear valve body by the spring. The pressure regulating mechanism is mounted on the cover of the ink storing chamber. The cover has a vent opening communicating the atmosphere with the air hole formed on the air groove of the rear valve body. The technical solution makes use of the sealing function acting on both the vent opening and the ink outlet by the pressure regulating mechanism to adjust the negative pressure which arises after the print needle has absorbed ink, such that the ink storing chamber is in the negative state when the ink cartridge is working. The spring force in combination with a sealing ball can cause the ink outlet to be sealed after the ink cartridge is detached from a printer. In order to realize that the ink storing chamber is in the negative pressure state when the ink cartridge is working, and the ink outlet is sealed after the ink cartridge is detached from a printer, the technical solution needs to add a pressure regulating mechanism. Accordingly, the technical solution complicates the structure, and further complicates manufacturing technology.
Furthermore, there is known an ink cartridge with another structure without a sponge. Chinese patent application No. 20041008321.3 discloses an ink cartridge comprising an ink tank for storing ink and a shutter mechanism arranged in the ink tank. The shutter mechanism includes a lever which can swing and which has one end provided with a shutter and the other end provided with a float. The weight and the volume of the float are set so that the first direction, in which the lever moves by the buoyancy and the gravity generated when the entire shutter mechanism is positioned in the ink, is opposite to the second direction, in which the lever moves by the buoyancy and the gravity when a part of the float protrudes from the ink liquid surface. A residual amount of the ink is indicated without being excessively affected by any disturbance such as the surface tension of the ink.